Please always mention the full part number so we can provide better assistance.

Regarding DAC0_OUT, you need to check the pinout table in the corresponding Reference Manual to see if the pin has a GPIO function assigned under ALT0.

- For example the KL25 manual shows this:

Then you can configure the pin as PTE30 and use it as GPIO. It can also be used for TPM module.

- On the other hand if you see the K64 manual then you would find this:

Then you can see that the pin does not have any digital function, only analog (DAC, Comparator and ADC).

- Now if you intend to use the DAC low and high digital values conversion to emulate a digital output then I guess it is possible but not an efficient approach. Also as you mentioned pay attention not to exceed the max output load current as specified in the datasheet. Below an example for K64: